[tip: x86/merge] x86/msr: Improve the comments of the DECLARE_ARGS()/EAX_EDX_VAL()/EAX_EDX_RET() facility

[tip-bot2 for Ingo Molnar]

The following commit has been merged into the x86/merge branch of tip:

Commit-ID:     76deb5452e79ab86eac699ae3b6a44ab9c437ffe
Gitweb:        https://git.kernel.org/tip/76deb5452e79ab86eac699ae3b6a44ab9c437ffe
Author:        Ingo Molnar <mingo@xxxxxxxxxx>
AuthorDate:    Fri, 02 May 2025 10:07:59 +02:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Fri, 02 May 2025 10:10:31 +02:00

x86/msr: Improve the comments of the DECLARE_ARGS()/EAX_EDX_VAL()/EAX_EDX_RET() facility

Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Uros Bizjak <ubizjak@xxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 arch/x86/include/asm/msr.h | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index 2ccc78e..27bc0b5 100644
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -37,20 +37,22 @@ struct saved_msrs {
 };
 
 /*
- * both i386 and x86_64 returns 64-bit value in edx:eax, but gcc's "A"
- * constraint has different meanings. For i386, "A" means exactly
- * edx:eax, while for x86_64 it doesn't mean rdx:rax or edx:eax. Instead,
- * it means rax *or* rdx.
+ * Both i386 and x86_64 returns 64-bit values in edx:eax for certain
+ * instructions, but GCC's "A" constraint has different meanings.
+ * For i386, "A" means exactly edx:eax, while for x86_64 it
+ * means rax *or* rdx.
+ *
+ * These helpers wrapping these semantic differences save one instruction
+ * clearing the high half of 'low':
  */
 #ifdef CONFIG_X86_64
-/* Using 64-bit values saves one instruction clearing the high half of low */
-#define DECLARE_ARGS(val, low, high)	unsigned long low, high
-#define EAX_EDX_VAL(val, low, high)	((low) | (high) << 32)
-#define EAX_EDX_RET(val, low, high)	"=a" (low), "=d" (high)
+# define DECLARE_ARGS(val, low, high)	unsigned long low, high
+# define EAX_EDX_VAL(val, low, high)		((low) | (high) << 32)
+# define EAX_EDX_RET(val, low, high)		"=a" (low), "=d" (high)
 #else
-#define DECLARE_ARGS(val, low, high)	u64 val
-#define EAX_EDX_VAL(val, low, high)	(val)
-#define EAX_EDX_RET(val, low, high)	"=A" (val)
+# define DECLARE_ARGS(val, low, high)	u64 val
+# define EAX_EDX_VAL(val, low, high)		(val)
+# define EAX_EDX_RET(val, low, high)		"=A" (val)
 #endif
 
 /*